Generally, horns may be used to amplify acoustic waves, as indicated by incorporation of horns in various musical instruments and early hearing aids, for example. Horns may also be used to manipulate radiation patterns of acoustic emitters, including ultrasonic transducers. Acoustic micro electro-mechanical system (MEMS) transducers, such as ultrasonic transducers including piezoelectric material, are typically more efficient than traditional transducers. However, due to their small size, MEMS transducers have lower effective output power, lower sensitivity and/or broader (less focused) radiation patterns, and thus benefit from being coupled to acoustic horn.
Acoustic horns affect the frequency response of the MEMS transducers and other miniature ultrasonic transducers, effectively acting as high-pass filters with corresponding cutoff frequencies based on the geometry of the acoustic horn. Also, the radiation patterns of the transducers may be manipulated by grouping the transducers into arrays, separated by predetermined distances, in order to provide a desired pattern. By controlling the separation and size of the acoustic horns and/or array elements, as well as the phase among them, cutoff frequencies and acoustic radiation patterns may be manipulated. However, the spacing among transducers is limited by the physical size of the transducers and acoustic horns, and the physical space available for mounting the transducers and acoustic horns.
FIG. 1A is a cross-sectional diagram illustrating an acoustic horn for an ultrasonic or MEMS transducer, for example. As shown in FIG. 1A, acoustic horn 100 is directly coupled to a single ultrasonic transducer 101 (e.g., in contact with the surface of the transducer 101). For example, the acoustic horn 100 may be physically attached to the transducer 101, e.g., by gluing, soldering or bonding. Alternatively, the combined acoustic horn 100 and the transducer 101 may be positioned relative to one another within a package, holding each element in place. The acoustic horn 100 provides better impedance matching, acoustic amplification or radiation pattern control than the transducer 101 alone, in both transmit or receive modes.
FIG. 1B is a cross-sectional diagram illustrating an alternative configuration of an acoustic horn for a MEMS transducer. As shown in FIG. 1B, acoustic horn 100 is coupled to a single ultrasonic transducer 101 by means of pressure chamber 115. This configuration may be implemented, for example, when the acoustic horn 100 is not able to touch the surface of the transducer 101. For example, the presence of wire-bonds may prevent a direct coupling, thus requiring the addition of the pressure chamber 115 for coupling the acoustic horn 100 and the transducer 101. Dimensions of the pressure chamber 115 are less than the acoustic wavelength corresponding to the transducer 101, as would be appreciated by one skilled in the art.